(a) Field of the Invention
This invention relates to a system for detecting different types of metal objects and more particularly, but not by way of limitation, to a non-obtrusive weapon detection system which allows an observer to discriminate between a handgun and other metal objects carried on a person.
(b) Discussion of Prior Art
Heretofore there have been a variety of patents describing the use of electromagnetic detection systems in underground mining applications and exploration. For example, U. S. Pat. Nos. 5,185,578, 5,066,917, 4,994,747 and 5,260,660 all to Stolarczykz, describe methods and apparatus for detecting underground electrically conductive objects, ore zones, etc. using transmitted electromagnetic energy. Both downhole receivers and downhole transmitters are used in these detection systems.
In U.S. Pat. No. 4,978,920 to Mansfield el al., a magnetic field screen is described. The screen is developed by a coil surrounded by a set of electrical conductors in a specific region in space. U.S. Pat. No. 4,959,559 to Ziolkowski discloses the use of wave propagation equations for producing localized pulses of wave energy. U.S. Pat. Nos. 4,821,023 and 4,866,424 to Parks describe state-of-the-art walk-through metal detectors using electromagnetic waves for detecting weapons.
None of the above mentioned patents describe the use of a non-obtrusive weapon detection system incorporating the recognition of specific metal objects through the determination of a characteristic time constant and comparison of this value with a data base containing corresponding values for a wide variety of metal objects. The pulses cause an eddy current to flow in a metal object on a person with a resultant scattered signal which allows an observer to identify objects that are threatening or non-threatening.